chore(ci): add CI workflow for manifest

Author: edwardzjl

.github/workflows/manifest-ci.yml

@@ -0,0 +1,35 @@
+name: Chatbot Manifest CI
+
+on:
+    push:
+      branches:
+        - main
+      paths:
+        - '.github/workflows/manifest-ci.yml'
+        - 'manifests/**'
+    pull_request:
+      types:
+        - opened
+        - synchronize
+      paths:
+        - '.github/workflows/manifest-ci.yml'
+        - 'manifests/**'
+    workflow_dispatch:  # Allows to trigger the workflow manually in GitHub UI
+
+jobs:
+  kustomize-istio:
+    name: Kustomize Istio
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions-hub/kubectl@v1.31.1
+        with:
+          args: kustomize ./manifests/overlays/istio
+  kustomize-knative:
+    name: Kustomize Knative
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions-hub/kubectl@v1.31.1
+        with:
+          args: kustomize ./manifests/overlays/knative-serving